The Contribution of Mergers and Accretion to Dark Matter Halo Assembly: An Excursion Set Theory Approach
Abstract
We study the relative contributions of mergers and accretion to the assembly of dark matter haloes within the framework of Excursion Set Theory (EST). We extend a variance-discretized merger-tree algorithm, which recursively reconstructs all branches of a complete merger tree and introduces a merger-ratio criterion for distinguishing mergers from accretion. The method is validated by comparing the resulting progenitor distributions with the analytical conditional first up-crossing distribution, showing excellent agreement over a wide range of halo masses and redshifts. We find that the accretion contribution depends strongly on the adopted merger-ratio threshold. For large merger ratios (MR=0.1--$0.25$), accretion accounts for up to ∼70% of the mass growth of massive haloes, whereas including all resolved mergers (MR=10−6) reduces the accretion contribution to ∼40%. These values are in good agreement with previous N-body simulation results. The accreted mass exhibits a nearly self-similar distribution in the mass-redshift plane, with the dominant contribution arising from progenitors in the range 10−3M0 ≲ M ≲ 10−1M0 and predominantly at 0.5 ≲ z ≲ 2. Our results demonstrate that EST-based merger trees provide an accurate and computationally efficient framework for investigating halo assembly and quantifying the relative roles of mergers and accretion in hierarchical structure formation.
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BibTeX
@misc{kameli2026contribution,
title = {{The Contribution of Mergers and Accretion to Dark Matter Halo Assembly: An Excursion Set Theory Approach}},
author = {Hamed Kameli},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.19312},
eprint = {2610.19312},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.19312},
}
RIS
TY - UNPB
TI - The Contribution of Mergers and Accretion to Dark Matter Halo Assembly: An Excursion Set Theory Approach
AU - Hamed Kameli
PY - 2026
DA - 2026/10/13
PB - arXiv
DO - 10.48550/arxiv.2610.19312
UR - https://arxiv.org/abs/2610.19312
AB - We study the relative contributions of mergers and accretion to the assembly of dark matter haloes within the framework of Excursion Set Theory (EST). We extend a variance-discretized merger-tree algorithm, which recursively reconstructs all branches of a complete merger tree and introduces a merger-ratio criterion for distinguishing mergers from accretion. The method is validated by comparing the resulting progenitor distributions with the analytical conditional first up-crossing distribution, showing excellent agreement over a wide range of halo masses and redshifts. We find that the accretion contribution depends strongly on the adopted merger-ratio threshold. For large merger ratios (MR=0.1--$0.25$), accretion accounts for up to ∼70% of the mass growth of massive haloes, whereas including all resolved mergers (MR=10^−6) reduces the accretion contribution to ∼40%. These values are in good agreement with previous N-body simulation results. The accreted mass exhibits a nearly self-similar distribution in the mass-redshift plane, with the dominant contribution arising from progenitors in the range 10^−3M_0 ≲ M ≲ 10^−1M_0 and predominantly at 0.5 ≲ z ≲ 2. Our results demonstrate that EST-based merger trees provide an accurate and computationally efficient framework for investigating halo assembly and quantifying the relative roles of mergers and accretion in hierarchical structure formation.
ER -